This invention relates to adjustable powder flow gates for rotary pellet presses and, more particularly, to adjustable powder flow gates having a spring loaded detent to maintain the gate in a fixed position during operation of the press.
Rotary pellet presses have been used for many years for such applications as forming pellets of medicines and the like and also in the nuclear power industry for forming pellets of uranium dioxide fuel for reactors. Rotary pellet presses generally have a rotatable turret having several dies at a fixed radius. A powder feed frame is positioned on top of a section of the turret, which rotates at about 10-24 rpm beneath the feed frame. The feed frame directs powder, or compacted granular material, that is dropped down by gravity from a feed chute to a limited area of the feed frame. An adjustable powder flow control gate attached to the powder feed frame provides adjustable control of the powder flow to ensure uniform die fill as the turret rotates beneath the feed frame. After passing the flow control gate, excess powder is wiped away from the die. The powder in the die is then compressed by punches from above and below the turret. The newly-formed pellets are pushed up out of the die and guided off the turret to a pellet take off disk by a bar angled in the pellet's path of motion.
The feed frames of the prior art suffer serious disabilities from their design. The flow control gates of the prior art are simple pieces of sheet metal formed so that the gate is oriented 90 degrees from the flat surface of the turret. A first piece of sheet metal is in a fixed position across a portion of the path of powder flow in the feed frame. A second, movable piece is attached to the first piece by a pair of mounting screws that fit through a slot in the second, movable piece. The gate is fastened to the feed frame and crude adjustment is accomplished by loosening the two mounting screws, moving the movable piece of the metal gate, and tightening the screws. This apparatus and method is imprecise. The sequence of loosening the screws, adjusting the gate and tightening the screws is a difficult operation because the press generally must be stopped during the sequence. Even though the press is stopped during the adjustment, the operator must reach into an area of the press where there are potentially hazardous powders. The effect of the adjustment is unknown until the press is restarted and some new product can be inspected. In addition, the screws often loosen as a result of vibrations of the operating press. Consequently, gate settings can spontaneously change, causing die fill inconsistencies, resulting in undesirable fluctuations of pellet density. This is a serious problem in the nuclear industry, where density tolerances are especially stringent.
There is therefore a need for a better means for adjusting and controlling powder flow to ensure uniform die fill in a rotary pellet press.